Picture-transmitting system



Jan. 14, 1930. L. G. ABRAHAM PICTURE TRANSMITTING SYSTEM Filed Aug. 18.1926 2 Sheets Sheet 1 //7 van/0r. Zea/74rd 6. Abraham y W Jan. 14, 1930.

L. G. ABRAHAM PICTURE TRANSMITTING SYSTEM Filed Aug. 18, 1926 2Sheets-Sheet 2 Ii: I llll'lovvl Patented Jan. 14, 1930 UNITED STATESPATENT OFFICE LEONARD G. ABRAHAM, OF BROOKLYN, NEW YORK, ASSIGNOB TOAMERICAN TELE- PHONE AND TELEGRAIEE COMPANY, A COBEOB-ATION OF NEW YORKPICTURE-TRANSMITTING SYSTEM This invention relates to speed controllingdevices and more particularly to means for controlling the movement ofsynchronously operating members'such as are employed in picturetransmission systems and telegraph systems.

It is an object of the present invention to improve the synchronizing oftwo movable members in a signaling system.

In order that the signals sent from the transmitting station may berecorded in the proper manner at the receiving station, it is thepractice in systems of the foregoing character to provide movingelements at the transmitting and receiving stations which move insynchronism. A rotating drum provides a convenient form upon which tohold the transmitting or recording element in picture transmissionsystems during the progressive scanning of the entire area of thepicture. Both the transparent picture to be transmitted and therecording film may be so positioned upon their respective drums thatthere is a portion of each drum, which is not effective in the thepicture characteristics. As the sending and receiving drums are rotated,these blank portions are presented to the light source once during eachrevolution of the drum. This portion of the revolution is termedthe'underlap period. It has been suggested heretofore that this underlapperiod be employed for transmitting impulses of carrier current ofincreased strength by means of which the driving motor may besynchronized.

In accordance with the present invention an arrangement is providedwherein synchronizing current transmitted during the underlap period isemployed to control the natural period of a resonance means at thereceivingstation as by varying the position of weights on the tines of atuning fork. In particular the invention contemplates an arrangement ofcommutators to variably operate magnets' to adjust the position of thesetuning Weights in the direction to bring the fork into synchronism withthat at the sending station.

In the embodiment of the invention disclosed, an impulse of carriercurrent of intransmission of impulses corresponding to Application filedAugust 18, 1926. Serial No. 130,062.

creased intensity is transmitted during the underlap period by thesending station, although the impulse need only be of a character todistinguish the underlapperiod from the picture transmission period. Atthe receiving station the tuning weights on the controlling fork areconnected by rods to a lever arm which is controlled by a pair ofmagnets. These magnets move the lever arm in opposite directions andthus move the tuning eoweights towards or away'from the tip of the fork.A commutating arrangement driven under the control of the fork providescircuits which are closed to the incoming signaling leads for a shorttime before and after the underlap period or the receiving drum. Each ofthese circuits contains a relay and if the receiving apparatus slowsdown or speeds up enough to close one of these circuits, at the sametime that the impulse of increased intensity is received, thecorresponding relay is operated and in turn operates the magnet whichmoves the weights in the desired direction.

The operation of the invention will be more 75 clearlyunderstood from aconsideration of the drawings in which Figure 1 shows a sending stationfor a picture transmission system, Fig. 2 shows a receiving station, andFig. 3 shows a modification of the commutating arrangement forming apart of the invention.

While it has been chosen to illustrate the in- Vention asapplied to asystem for transmitting pictures, it is understood that the invention isapplicable to any signaling system wherein synchronism is desired andthe driving means is controlled by a tuning fork. For a description of acomplete system of the type disclosed, reference may be made to PatentNo. 1506,22? granted to J. Horton et 211., Nov. 9, 1926.

Referring to Fig. 1, there is shown a driving motor 35, which may be ofany type adapted to operate at a'relatively constant speed. This motoris preferably a phonic wheel or other tuning forkcontrolled motor andmay be started in operation manually.

When magnet 20 receives a starting impulse, the spring actuated clutchmember 18 is released. The clutch member thereupon cooperates with gears10 and 24, whereby gears 16 and are rotated. Mounted on the shaft 26,rotated by gear 16, is a drum 15, adapted to rotate with said shaft. Theframe 84, in which the shaft 12 is rotatably mounted, is adapted to movelongitudinally along the base plate 93, when thread 17 rotates inthreaded.

bearing 94. Gear 25 by means of the sleeve 92 is so mounted on shaft 95as tomove longitudinally and integrally with the frame 84. Thus whenshaft 95 rotates, rotatory and longitudinal movements are imparted togears 16 and-25. The gears 16 and 25 are so designed as to allow for theproper ratio between the ro- V photoelectric, or other light sensitive,cell 22,

which has its resistance varied in accordance with the characteristicsof the picture. The cathode and anode of this cell are connected to theinput circuit of'amplifier 100 so that the variations in the resistanceof the-cell cause corresponding variations of current flow 1n the 1nputand output circuits of the amplifier. The output circuit of. amplifier100 is connected to the modulator 102, whereby the amplitud ofthecarrier waves generated by oscillator 103 are modulatedandare thenimpressed on the line L after passing tllsiiough the, transmittingterminal amplifier The picture is so mounted on drum 15 that between theends of said picture there is an opaque portion 23 which intercepts therays of light from the source 21 for a comparatively short period,called the underlap period, during each revolution of drum '15. Duringthis underlap period, therefore, the carrier waves are not modulated inaccordance with the picture characteristics, but are changed in.amplitude for synchronizing pur poses, as will be described hereinafter.

From an inspection of Fig. 1, it will be noted that during the period oftransmission of the picture characteristics that the lower right winding51 of transformer 52 alone is effective to cause the carrier waves to bemodulated. thus limiting the maximum am-' yond their amplitude duringthe picture transmission period.

For a complete disclosure of the operation of modulator 102, referenceis made to the above identified patent to J. W. Horton, et a1. At thereceiving station shown in Fig. 2,

the modulated carrier waves are received over line L and-are amplifiedby receiving terminal amplifier 104 and" picture amplifier 105, afterwhich the impulses affect the light valve 11, or they may be employed inany other manner for reproducing the picture. As shown, the drivingmotor 54, which is preferably similar to motor 35, is employed forrotating shaft 87, which is suitably geared to the crown wheel 28. Adrum 29, similar to dI'IIIIl 15, is rotated by gear 30 when the springactuated clutch member 31 is released by actuation of the start magnet99. The portion 33 of the drum included between the ends of the picturecorresponds to the portion 23 of drum 15.

In order to avoid distortion in the received wave, it is necessary thatdrums 15 and 29 rotate in synchronism. At the sending station, motor 35is controlled by the fork 86, while at the receiving station, fork 68controls the operation of motor 54. Each of the controlling tuning forks86 and 68, once motion is imparted thereto, continues to vibrate at itsnatural period under control of a selfinterrupting circuit. For example,contact 88 provides a self-interrupting circuit for the fork 86. Thiscontact when closed completes a circuit from battery through the windingof the driving magnet 89. Magnet 89 is, therefore, energized anddeenergized in correspondence with the natural frequency of the tines offork 86. Each of the forks is also provided with sets of contacts forcontrolling the operation of the associated motors 35 and 54, in thewell known manner.

.Motor 35 at the sending station also controls a shaft comprisingsections 36, 37, etc., which are insulated from each other by means ofthe insulating segments 38 and 50. Rigidly and conductively secured tothis shaft are a number of disc-like commutators 39, 40, 41, 42 and 43.The shaded portion of each disc represents insulation and the unshadedportion represents conducting material. .Ar-

rangedfor cooperation with the commutators are'brushes 45, 46, 47, 48and 49. It will be noted, therefore, that a circuit is prepared by meansof brush 46 and commutator 40 during the entire revolution of the shaft.Brushes 45, 48 and 49 are so positioned that they make contact with theconducting portions of their respective commutators only during thatportion of a revolution which corresponds to the underlap period of,drum 15. Similarly brush 47 is positioned soas to be insulated fromtheshaft section 37, only during the underlap period. The angular widthof the conducting segments on commu-- T I tators 39, 42 and 43, and ofthe insulating segment of commutator 41 may be such as to providecommutation during a complete underlap period or during only a portionof this period as may be necessary for synchronizing purposes.

The .motor 35 is adapted to be continuously operated so that brush '45closes a circuit through segment 44 and shaft section 37 once everyrevolution, namely, during the underlap period. During this period,therefore, a

circuit may be traced from the upper conductor of line L, brush 46 andcooperating commutator shaft section 37, segment 44 and brush 45, rightwindings of transformer 52, thence through the lower conductor of lineL. It will be noted that during the underlap period brush 47 rests on aninsulating segment, and conse uently the carrier waves'are unmodulated.gince both windings of transformer 52 are thus effective during theunderlap eriod, the carrier current impressed on line JWlll have agreatly increased amplitude. During the major portion of the revolutionof drum 15, and assuming that no picture signals are being transmitted,brush 45 rests on insulation and brush 47 rests on conducting material.Therefore, the upper winding 53 of the transformer '52 is renderedineffective. The output circuit of the modulator is closed by means of acircuit completed from'the .upper conductor of line L, brush 46 andcooperating commutator 40, shaft section 37, brush 47 and commutator 41,through the output winding of modulator 102, thence to the lowerconductor of the line. The carrier current impressed on the line L,hy'means of winding 51, has a constant amplitude while no picture isbeing transmitted, but when pictures are being transmitted, the currentis.

"weights may be made by means of turn buckles 126 and 127. The frequencyof vi bration of the fork may, by these means, he brought very closelyto that of fork 86. To bring the synchronism of the two forks under thecontrol of fork 86, the crank arm 128 is moved under controlof impulsesfrom the sending station.

Crank arm 128 is pivotedon pin 129 and has one arm connected with yoke123. The opposite arm is slidably mounted on armature 130, which isacted upon bymagnets 131 and 132. The movement of armature130 towardmagnet 131 draws the weights 119 and 120 nearer the base of the forkwhereas the action of magnet 132 forces them away from the base. Thesemovements are, of course, quite small and serve to adjust the frequencyof the fork between the desired limits. A

dash pot 146 is provided for holdin arm 128 in any position. Magnets 131an 132 are connected in series to battery 144 so that they normallyexert equal and opposite forces on armature 130 when it is in thecentral position. Alternating current-relays 61 and 71 control shuntsabout magnets 131 and 132 and are operated by the impulses of increasedcarrier current from the sending station when their circuits are closedby commutating discs 111 to 118. When either of the magnets is shunted.the other magnet exerts suflicient force to move the armature 130 towardthe unshunted ma net.

According to one em odiment of the invention the commutating discs 111to 118 are driven directly by motor 54. The shaft carrying these discsis divided into sections by insulating segments 90, 106 and 107. Section108 carries discs 111 to 113; section 109 carries discs 114 and 115;section 110 carries discs 116 to 118. As the discs rotate, a circuit isclosed just before the underlap period from conductor 133, brush 134,conducting segment 135 of disc 112, shaft section 108, conductingsegment of disc 111, brush 136 through the winding of relay 61, brush137, conducting segment 138 of disc 116, shaft 110, disc 117 toconductor 139. A similar circuit is closed just after the underlapperiod which extends from conductor 133, segment 140 of disc 112, shaftsection 108, disc 113, brush 141, brush 142, disc 114, shaft section109, disc 115, brush 143, winding of alternating current relay 71 tobrush 137 conducting segment 147 of disc 116, shaft 110, disc 117, andthence to conductor 139. During the underlap period brushes 136 and 143engage insulating segments of the commutating-discs upon which they ridepreventing the closure of the circuits of relays 61 and 71. Discs 117and 118 serve to connect light valve 11 to the amplifier 105 forrecording-the picture current.

From the above description it will be apparent that as long as motors 54and 35 remain in synchronism, the increased carrier current sent outduring the underlap period will be ineffective at the receiving station.

If now the tuning fork 68 slows down enough 'to'close' the circuit ofrelay 61 during the underlap period at the sending station, the

impulse of carrier'current of increased intensity will pass throughrelay 61 and that relay will operate. When relay 61 is operated, a shuntis closed through armature 145 around the winding of magnet 132. Thepull on armature 130 is thus unbalanced and the armature is drawntow'ardmagnet-131. This movement of armature 130 is transmitted by crankarm 128 to yoke 123, drawing weights 119 and 120.away from the tip ofthe fork 68 and increasing the speed of its vibration.

Arm 129 is acted upon by a mechanical. de-

vice 146 which holds the arm in place except when-acted upon by one ofthe magnets 131- or 132 alone.

If the speed of the fork 68 should be increased out of synchronism, thecircuit above traced will be closed while picture current is beingreceived, but this current will not oper ate relay 61 since relay 61 ismarginal, as is relay 71. The circuit above traced for relay 71 will beclosed during the underlap period at the sending station and relay 71will be operated by the increased current received. The operation ofrelay 71 shunts magnet 131 permitting magnet 132 to draw armature 130toward itself and force the weights nearer to the-tip of the fork, thusslowing the speed of the fork.

The circuit of the light valve is held open for a period extending froma definite time before the underlap period to a definite time after theunderla-p period. The light valve therefore does not receive theincreased carrier current.

When it is desired to transmit pictures, tuning forks86 and 68 areinitially set in mo-- tion, and motor 35 at the sending station andmotor 54 at the receiving station started in operation. Shafts 36 and.55 are thus rotated, and unmodulated carrier current generated byoscillator O, is impressed on the line L by means of the winding 51 oftransformer 52. After an interval, due to the action of relays 61 and 1as above explained, motors 35 and 54 are synchronized. Shafts 110'and 87are also driven but are inefiective sinc'e'the clutch members 18 and 21have been manual-" lylocked open at this time.

Key 76 is next operated to close contacts 7 7 and 78. If this key isthrown during the 20 immediately locks under control of key 85. As soonafter key 76 is operated as the underlap period occurs, the outputcircuit of the modulator is shunted by means of a path traceable fromthe upper terminal of the modulator output coil, condenser 79, contacts77 and 7 8 of key 7 6, brush 48 and conducting segment of commutator 42,brush 49 and conducting segment of commutator 43 to the" lower terminalof the modulator output coil. Condenser 79 is of such capacity as toreduce the line currentto substantially zero value. With magnet 20locked, should key 76 be held operated after the occurrence of the nuderlap period. the modulator output coil, remains shunted over a pathtraceable from the upper terminal of said output coil, condenser 79,contact 77 of key 76, conductor 80, locking contact of magnet 20, to thelower termi-v nal of the modulator output coil. The reduction of currentin the line as above .described serves to set the receiving apparatus inreadiness for the modulated carrier by -operatingflmagnet 99, as isfully described in the patent to Hortonet al., referred tohere- .willrender the operation gle revolution of the drum 15, then, when brushes48 and 49 next make contact with their cooperating conducting segments,the condenser 79 short-circuits the output terminals of the modulator102. The synchronizing current is however applied to the line L by meansof both windings of transformer 52 and brushes 45 and 46 as hereinbeforedescribed. 1 7

Should the brushes 48 and 49 be in contact with their conductingsegments that is, if the modulated current flows in the line L until theunderlap position is passed, when brushes 46 and 47 complete a circuitthrough their respective commutators'.

At the. receiving station the interruption of the carrier current causedby the operation i ofthe key 7 6 brings about the energization of magnet99 as described in the patentto Horton et al., referred to hereinbefore.Magnet 99 attracts the pivoted arm 32 whereby.

the clutch member 31 is released to cause the rotation of gear 30 anddrum 29. When key 76 at the sending station is restored to normal, theshunt circuit is removed from the output terminals of the modulator andcarrier. waves modulated in accordance with the picture characteristicsare impressed on line L. Y

In a modified embodiment of the invention, the commutating arrangementis mounted at one end of the drum 29. Fig. 3 shows a possiblearrangement of the segments and brushes, the shaded portion representingm- I 'sulation, and the clear portions, conducting material. The brushes336, 334, etc., are

represented diagrammatically by the dots shown in the center of theunderlap region 148 and may be mounted in any suitable manner oncarriage 149. Annular sections of the face of the drum of Fig. 3(indicated by dotted lines) correspond to the separate discs of Fig. 2.The rings and brushes have been given the same numbers as in Fig. 2 withthe initial digit 3 instead of 1. A comparison of Figs. 2 and-3 withthis numbering in mind of Fig. 3 self-explanatory.

What is claimed is: v 1. In a synchronizing system, two rotatablemembers to be maintained in synchronism and located at differentstations respectively, a transmission channel connecting said stations,means under the control of the rotatable member at one of said stationsonly, for impressing synchronizing current impulses on said transmissionline, a tuning fork for controlling the speed of the second member,weights for varying the speed of said tuning fork, and means operated bythe synchronizing impulses received over said transmission channel whensaid members are out of synchronism to move said weights to return saidsecond member to synchronism with said first member.

2. In a synchronizing system, two motors to be synchronized, and locatedat different stations respectively, a transmission channel connectingsaid stations, means under the control of one of said motors only forsending synchronizing current impulses during a predetermined portion ofeach revolution of said motor, a tuning fork for controlling the speedof the second motor, weights for determining the speed of said tuningfork, means associated with said second motor for blocking said impulseswhen said motors are in synchronism and means for rendering saidimpulses effective when said motors are out of synchronism to move saidtuning weights to return said second motor to synchronism with saidfirst motor. a

3. In a synchronizing system, two motors to be synchronized and locatedat different stations respectively, a transmission channel connectingsaid stations, means under the control of one of said motors forimpressing synchronizin current impulses on said transmission lineduring a predetermined portion of each revolution of said motor, atuning fork for controlling the speed ofa second motor, weightsforcontrolling the speed of saidtuning fork, means for varying the positionof said weights on said tuning fork, a commutator associated with saidsecond motor effective when said-motors are in synchronism to block saidimpulses and effective when said motors are out of. synchronism tooperate said Weightpositioning means to return said second motor tosynchronism with said first motor.

4. In a system for synchronizing motors, means under the controlof onemotor for sending synchronizing impulses of characteristic amplitudeduring a redetermined portion of each revolution 0 said motor, a-tuningfork for controlling the speed of-a second motor, weights for regulatingthe speed of said tuning fork, a pair ofvrelays responsive only toimpulses of said characteristic amplitude to control said weightpositiomn means a commutator associated with sa second motor effectivewhen said motors are in chronism to block said impulses and ea tive whensaid motors are out of synchronism to operate the pro r one of saidrelays to return said secon motor to synchronism with said first motor.

5. In a picture transmission system, a transmission line, a sendingstation, a receiving station, means for scanning a picture in saidrecording means to synchronism with said scanning means.

6. In a picture transmission system, a transmission line, a sendingstation, a receiving station, means at said sending Sta-- tion forscanning a picture in successive linear elements means for sending acurrent correspon 'ng to said linear elements, means effective at theend of the scanning of each linear element for increasing the amplitudeof said current, means for recording said picture current at saidreceiving station, a commutator at said receiving station, means forsimultaneously driving said recording means and said commutator, a pairof marginal relays at the receiving station; means controlled by saidcommutator when said scanning means and said recording means are out ofsynchronism to direct said increased current to one of said mar a1relays, and means under the control 0 said relays fbr returning saidrecording means to synchronism with said scanning means.

7. In a picture transmission system, a trans mission line, a sendingstation, a receiving station, means at said sending station for scanninga picture in sucessive linear elements, means for sending a currentcorresponding to said linear elements, means effective at the end of'thescanning of each linear element forincreasing the amplitude of saidcurrent, means for recording said picture current at said receivingstation, a commutator carried by said recording means, a pair ofmarginal relays at the receiving station, means controlled by saidcommutator when said scanning means and said recording means are out'ofsynchronism to direct said increased current to one of said marginalrelays, and means under the control of said relays for returning saidrecording means to synchronism with said scanning means.

8. In a picture transmission system, a transmission line, a sendingstation, a'receiving station, means at said sending station for scanninga picture in successive linear elefective at the end of the scanning ofeach linear element for increasing the amplitude of said current, meansfor recording said picture current at said receiving station, ac0mmutator carriedby said recording means, a tunin fork for controllingthe speed of said recor ing means, Wei hts for controlling the speed ofsaid tuning ork, means for varying the position of said weights on saidtuning fork, a pair of marginal relays at said receiving station, meanscontrolled by said commutator when said recording means and saidscanning means are out of synchronism to direct said increased currentto one of said marginal relays to operate said weight positioning meansto restore said recording means to synchronism with said scanning means.

9. In a synchronizing system, a plurality of stations, speed controlmeans comprising variable resonance means at one of said stations, meansat saidone station for varying the natural period of said resonancemeans over a range of values between fixed limits, and means at. anotherof said stations for controlling said last mentioned means when there isa departure from synchronism.

10. A synchronizing system comprising motive means at each station forthe elements to be synchronized, constant, speed means comprisinvariable resonance means associated wit the motive means at one of saidstations, means at said one station for varying the natural period.- ofsaid resonance means over a range of values between fixed limits, andmeans at another of said stations for controlling said last mentionedmeans when there is a departure from synchronism.

11. In a synchronizing system, a plurality of dynamo electric machinesto be maintained in synchronism and located at di fl'erent stations,respectively, means comprising a variable resonance means associatedwith a dynamo electric machine at one of said stations for maintainingsaid machine at a substantially constant speed, and means at anotherstation for causing a change in the constants of said variable resonancemean hen there is a departure from synchronism, to increase or decreasethe speed at which the dynamo electric machineis maintained constant. vr

In testimony whereof, I have signed my name to this specification this17th day of.

August, 1926: LEONARD G. ABRAHAM.

